The present invention generally relates to light transmission paste and a metallic copper deposition method using it.
A circuti pattern formation in the conventional hybrid IC was effected by a printing method on an alumina ceramic substrate. The fundamental component in the printing method is composed of a screen 1 which has an empty hole corresponding to the circuit pattern to be drawn on the substrate and a squeegee 2 as described in FIG. 5. Also, the screen 1 is retained parallel to the substrate 3 and in a position approximately 0.25 mm through 2.0 mm from the surface of the substrate 3. Conductive paste 4 which becomes patterns 5 is placed on the screen 1. The conductive paste 4 is depressed by the squeegee 2 moving along and depressing the screen 1. As a result, the conductive paste 4 is moved onto the substrate 3 from the empty hole portion in the screen 1, and the patterns 5 are formed on the substrate 3.
It is proposed recently that the patterns should be formed on the substrate by a drawing method. The conductive paste 4 is filled into a paste cartridge 7 as shown in FIG. 6. The paste cartridge 7 is formed in a cylindrical shape, is contracted in its lower end portion, and is provided with an empty hole 0.06 through 2 mm in diameter. The paste which is in the cartridge having a certain diameter hole at its lower end portion is subject to pressure application through the air or the like upon the upper end portion of the paste cartridge 7. By the movement of the paste cartridge 7 while the paste is being discharged, the pattern 5 of a given line width is drawn.
In the printing method, the screen 1 must be replaced also after this when the pattern to be obtained has been changed. The screen 1 is also expanded through a certain number of printing operations if the pattern is the same. Thus, a positional shift is caused in the printed pattern 5. Therefore, the screen must to be exchanged on the A uniform screen 1 is not always available, when the screen must to be exchanged, because of the working accuracy of the screen frame, the accuracy necessary when the screen 1 is pasted on the frame, and so on. Therefore, in the exchange of the screen 1, adjustments such as new positional alignment, parallel arrangement of the substrate 3 and the screen 1 are necessary. But it takes about thirty minutes at least for the adjustment, thus reducing the operation rate of the hybrid IC production line.
When the pattern 5 is designed, and tested, about four days are required to make the screen, so that the development period is caused to be extended.
In the drawing method, a program with pattern coordinates having been inputted has only to be changed even when there are changes in the pattern 5, so that these changes hardly cause stoppage of the hybrid IC production line. But the empty hole in the tip end portion of the paste cartridge 7 at this time is restricted to 0.06 through 2 mm in diameter, and also the pattern is basically formed with lines, with a disadvantage that the productivity is extremely lower as compared with the printing method.
Recently a method has been conducted of making a pattern forming circuit which does not reduced the operation rate of the hybrid IC production line, even in a case where a substrate of a different pattern is obtained, and further this method is available even in mass production. In one example, the disproportioned reaction of cuprous oxide is used.
The reaction expressed by EQU 2Cu.sup.+ .revreaction.Cu.sup.o +Cu.sup.2+ ( 1)
is caused in a portion where light of 280 nm through 640 nm has been applied under a weak acidic condition such as 0.002N sulfuric acid aqueous solution so as to produce metallic copper, so that the metallic copper may be selectively educed and the pattern is formed.
In order to cause the disproportioned reaction of the cuprous oxide, the light of 280 nm through 640 nm is required to be applied under the weak acidic condition. As shown in FIG. 7 (A), the cuprous oxide 8 was applied on the substrate 3 forming the pattern. Then, as shown in FIG. 7 (B), it was dipped into a weak acidic aqueous solution such as dilute sulfuric acid or the like, and light from a light source 11 is applied upon it a pattern formed by the mask 10, thus obtaining the pattern 12.
But only half of the cuprous oxide applied as shown in the equation (1) became the metallic copper in the disproportioned reaction of the cuprous oxide. It was difficult to raise this ratio. The reduction in the final density of the metallic copper caused the electronic circuit have an extremely high resistance value. Therefore, it is necessary to raise the density of the metallic copper by another method. One of the methods to be generally taken at this time is a physical development. As shown in FIG. 8 (A), the cuprous oxide which was not reacted with an aqueous solution of sodium thiosulfate or the like was removed. The pattern 12 existing on the substrate 3 was retained in a metallic salt aqueous solution 13 in a reducing atmosphere as shown in FIG. 8 (B) so that as to grow around the metallic the component metal of the metallic salt grows around the metallic copper as a nucleus, thus producing a copper pattern 14 of high density.
In the disproportioned reaction of the cuprous oxide under the weak acidic aqueous solution by this method, the thickness of the weak acidic aqueous solution on it is required to be constant across the whole face with the cuprous oxide existing on it if a precise pattern is to be formed, because the refractive index of the light in the air and within the weak acidic aqueous solution is different. Therefore, the light cannot be applied upon the cuprous oxide until the cuprous oxide put into the weak acidic aqueous solution becomes certain with respect to the weak acidic aqueous solution surface. Thus, it was considerably difficult to use this method for the making of the pattern. Since the acidic aqueous solution caused the corrosion of metal, it was difficult to use it in the production line.
In the physical development using the metallic salt aqueous solution within the production line, problems such as metallic salt aqueous solution exchange, waste processing and so on are undesirably caused.